Our overarching goal is to understand the process of human placental trophoblast differentiation during the latter half of pregnancy, and the adaptive response of trophoblasts to injury. The clinical consequences of abnormal trophoblast differentiation and placental dysfunction are far-reaching, typically leading to intrauterine fetal death or fetal growth restriction. Newborns surviving these insults are at risk for lifelong complications, including neuro-developmental dysfunction and a greater incidence of the adult metabolic syndrome. Whereas the association of these conditions with placental dysfunction has been scrupulously substantiated, the mechanisms underlying trophoblast differentiation and adaptation to injury are poorly understood and insufficiently explored. Reflecting our poor understanding of the pathophysiology of fetal growth restriction, there is no effective treatment for this condition. The only intervention to prevent further fetal damage is delivery, which is designed to prevent further injury, yet commonly leads to prematurity. The recent discovery of microRNA (miRNA) adds a new dimension to cell-specific regulation of transcript and protein expression. Our knowledge of endogenous miRNA expression and its role in the development and function of mammalian tissues is rudimentary. Specifically, information regarding placental miRNA is scarce. Information gleaned from current studies in other tissues, bolstered by our own recent data, supports our hypothesis that the expression and function of discrete types of human placental miRNA govern trophoblast differentiation and adaptation to injury. Building on our preliminary data, we will mechanistically decipher the action of miRNAs that are regulated during trophoblast adaptation to injury. Through these analyses we seek to transform our understanding of trophoblast dysfunction during the second half of human pregnancy, and explore previously unknown pathways in trophoblast response to injury. Our proposal is unique, because (a) we focus on novel pathways of gene regulation that have not been interrogated thus far in the placenta, (b) we build our planned investigation on an unbiased, cutting edge technology in high-throughput miRNA-microarray analysis, combined with comprehensive mRNA arrays and proteomics, designed to define relevant miRNA targets in the placenta, and the regulatory function of these miRNA, and (c) we utilize innovative tools to establish a cause and effect relationship, not mere associations. Our data will not only illuminate the molecular underpinning of trophoblast adaptation to injury, but may also lay the foundation to future translational research into novel diagnostic and therapeutic approaches for women with pregnancies complicated by placental dysfunction.